One example of a conventional image pickup apparatus capable of measuring distances is an image pickup apparatus of Patent Document 1. FIG. 38 is an exploded perspective view of the image pickup apparatus of Patent Document 1. FIG. 39 is a diagram for explaining an image pickup block of the image pickup apparatus of Patent Document 1. As shown in FIGS. 38 and 39, an image pickup apparatus 901 that is a compound-eye image pickup system includes an iris member 902, an optical lens array 903, a light shielding block 904, an optical filter 906, and an image pickup unit 907. In the image pickup apparatus 901, the iris member 902 having four openings 902-1, 902-2, 902-3, and 902-4 and the optical lens array 903 having four optical blocks (lenses) 903-1, 903-2, 903-3, and 903-4 constitute four image pickup optical systems. Light beams having passed through the respective image pickup optical systems form images on four image pickup blocks 907-1, 907-2, 907-3, and 907-4, respectively, on the image pickup unit 907. The image pickup unit 907 constituted by, for example, a CCD sensor is formed on a semiconductor substrate 910 together with a drive circuit 908 configured to drive the image pickup unit 907 and a parallax calculating circuit 909 configured to calculate information regarding parallax among images taken by the plurality of image pickup blocks 907-1 to 907-4.
As described above, the light beams having passed through the openings 902-1 to 902-4 of the iris member 902 are refracted by the lens 903-1 to 903-4, respectively. Then, the light beams pass through the light shielding block 904 and the optical filter 906 to form images on the image pickup blocks 907-1 to 907-4. Then, for example, a degree of similarity between the image taken by the image pickup block 907-1 and the image taken by the image pickup block 907-2 is calculated using block matching. A parallax d is calculated based on the degree of similarity, and a distance L is calculated based on the parallax d as shown by Formula (1) below. In Formula (1), f is a focal length of each of the lenses 903-1 and 903-2, B is an interval between optical axes of the lenses 903-1 and 903-2, and p is a pixel pitch of the image pickup unit 907 in a direction in which the optical axes of the lens 903-1 and 903-2 are opposite to each other.L=fB/pd  (1)
However, the lens array 903 deforms with changes in temperature, and this changes the interval B between the optical axes of the lenses. Therefore, if the temperature changes, the distance cannot be calculated properly.
An image pickup apparatus capable of dealing with such temperature change is disclosed in Patent Document 2. Since the image pickup apparatus of Patent Document 2 is the same in configuration as the image pickup apparatus of Patent Document 1 except that the image pickup apparatus of Patent Document 2 includes a temperature sensor, it will be explained in reference to FIG. 38. The image pickup apparatus of Patent Document 2 includes the lenses 903-1 to 903-4 arranged at regular intervals and a temperature sensor configured to measure a temperature T of a portion in the vicinity of the lenses 903-1 to 903-4. The image pickup apparatus of Patent Document 2 uses the temperature T to correct images I1 to I4 taken by the image pickup blocks 907-1 to 907-4.
More specifically, the image pickup apparatus of Patent Document 2 calculates an amount (T-T0) of change in temperature with respect to a reference temperature T0, and as shown by Formula (2) below, calculates an amount z of change in the interval B between the optical axes of the lenses due to the temperature change based on a difference (aL−aS) between a linear thermal expansion coefficient aL of the lens array and a linear expansion coefficient aS of the image pickup unit 907. Then, using the image I1 taken by the image pickup block 907-1 as a reference as shown by Formula (3) below, the images 12, 13, and 14 taken by the image pickup blocks 907-2, 907-3, and 907-4, respectively, are corrected by the change in the interval between the optical axes of the lenses as shown by Formulas (4), (5), and (6). Here, the lenses 903-1 and 903-2 are arranged away from each other in an x-axis direction, the lenses 903-3 and 903-4 are arranged away from each other in the x-axis direction, the lenses 903-1 and 903-3 are arranged to be spaced apart from each other in a y-axis direction, and the lenses 903-2 and 903-4 are arranged to be spaced apart from each other in the y-axis direction. Then, p is the pixel pitch of the image pickup unit 907, and is the same in the x-axis direction and the y-axis direction. Each of I1(x, y), I2(x, y), I3(x, y), and I4(x, y) denotes luminance of each image at coordinates (x, y). As compared to the lens 903-1, the lens 903-2 moves by z/p pixels in the x-axis direction due to the temperature change. Therefore, as shown by Formula (4), I2(x, y) is corrected so as to move by z/p in the x-axis direction. Moreover, as compared to the lens 903-1, the lens 903-3 moves by z/p pixels in the y-axis direction due to the temperature change. Therefore, as shown by Formula (5), I3(x, y) is corrected so as to move by z/p in the y-axis direction. Further, as compared to the lens 903-1, the lens 903-4 moves by z/p pixels in the x-axis direction and by z/p pixels in the y-axis direction due to the temperature change. Therefore, as shown by Formula (6), I4(x, y) is corrected so as to move by z/p pixels in the x-axis direction and by z/p pixels in the y-axis direction.z=B(aL−aS)(T−T0)  (2)I1(x,y)=I1(x,y)  (3)I2(x,y)=I2(x+z/p,y)  (4)I3(x,y)=I3(y,x+z/p)  (5)I4(x,y)=I4(x+z/p,y+z/p)  (6)    Patent Document 1: Japanese Laid-Open Patent Application Publication 2003-143459    Patent Document 2: Japanese Laid-Open Patent Application Publication 2002-204462